I. Field of the Invention
The invention pertains to the field of fluoropolymer hoses and tubes such as fluoropolymer composite pipes such as those used in fuel lines.
II. Description of the Prior Art
With the advent of increased concern over evaporative fuel emissions standards, there has been an increasing need for fuel lines that meet increased evaporative emission requirements while at the same time having high chemical and electrostatic discharge resistance. Further, in order to be economical, any fuel line must be able to be produced in large quantities at a low cost. A desired fuel line likewise should have appropriate physical properties including but not limited to sufficient tensile strength and kink resistance, or the ability of the fuel line to retain a particular shape upon bending.
Fuel line hoses of a variety of materials have been suggested over the years. Tetrafluoroethylene has been utilized and has excellent and outstanding high temperature and chemical resistance. "Hose Technology," publisher: Applied Science Publisher, Ltd., Essex England, by: Colin W. Evans, pages 195-211. Nylon has also been utilized as a hose composition. However, fluorinated polymers are difficult to use because it is difficult to adhere other materials to them in order to form desirable composites.
U.S. Pat. No. 4,933,060 discloses surface modification of fluoropolymers by reactive gas plasma. The reference, however, further indicates that in order to have sufficient bonding, adhesives must be utilized prior to the application of an additional layer. Suitable adhesives are epoxies, acrylates, urethanes, and the like.
U.S. Pat. No. 4,898,638 teaches a method of manufacturing flexible gaskets which withstand chemical agents. Flexible gaskets are prepared in which one film of PTFE (polytetrafluoroethylene) is directly applied onto a sheet of raw rubber and the sheet of rubber together with the film of PTFE is subjected to heating and pressure suitable for causing the rubber to vulcanize. Use of adhesives in the bonding of fluoropolymers is likewise described in U.S. Pat. No. 4,743,327, and their use is required to make the development operative. Activating fluoropolymers utilizing ammonia gas is taught in U.S. Pat. No. 4,731,156.
None of the prior art describes a fluoropolymer with a layer of a thermosetting or thermoplastic polymer, preferably an elastomer, that is integral with and chemically bonded to the fluoropolymer, which when combined in a multi-layered composite hose or pipe, has desirable electrostatic discharge resistance, hydrocarbon evaporative emission resistance, and flexibility. Further, the prior art suggests the need for adhesives to firmly and fixedly join plastic layers. This invention does not have as an essential requirement that additional adhesives are needed in joining the fluoropolymer layer to the thermosetting or thermoplastic elastomer because there exists a chemical bond between the fluoropolymer and the thermosetting or thermoplastic polymer layers.
Polymer surfaces typically lack the irregular structure necessary to achieve an effective mechanical bond. Therefore, methods such as etching or scuffing have been used to physically "roughen" the substrate surface. This invention however, by incorporating a chemical bond, does not require this mechanical alteration of the surface. It can be shown through various microscopic techniques (i.e. SEM) that no significant changes occur to the physical structure of the substrate surface by exposure to the charged gaseous atmosphere utilized in this invention. Furthermore, bonding has been achieved by this method with materials such as thermoset elastomers which typically do not have processing viscosities sufficiently low to achieve adequate bond strength strictly by mechanical means.
It is an object of the present invention to have a fuel pipe or tube that has a fluoropolymer substrate that can be activated sufficiently to be able to have an integral and chemically bonded top coat or layer of a thermosetting or thermoplastic elastomer.
It is also an object of the present invention to prepare a fluoropolymer composite by extruding a multi-layered fluoropolymer substrate, one layer of which has desirable chemical, permeation, and electrostatic discharge resistance, and on top of the fluoropolymer layers would be an extruded thermosetting or thermoplastic elastomer layer.